It is understood in the art that a certain safety distance while driving must be maintained between cars to avoid collisions. This is because the response of a driver to an emergency is limited by his natural physical condition and acquired driving skill.
Some simple formulas for calculating the safety distance between cars can be obtained. One example of a formula that calculates safety distance is (m)=car speed (km/hr).div.10.times.car length (m). The safety distance thus derived, however, is impossible to maintain since the driver is unable to estimate it accurately without the help of suitable equipment. Moreover, the safety distance is impossible to maintain since other cars can intrude at random within the safety distance.
Currently, due to the development of anti-skid braking systems (ABS) the braking distance is effectively shortened. However, when a car reduces speed quickly, it is susceptible to collision in the rear by a car which is not equipped with an ABS. Many cars are installed with a third brake light at the rear window to improve the warning to the rear car driver. Nevertheless, collision accidents are likely to occur due to failure to maintain safety distances. Therefore, the development of an apparatus which is able to provide the driver with accurate information on the front and rear safety distance becomes essential.
Some drivers apply the method of slightly stepping on the brake pedal to light up brake lights for warning the rear car, which results in more fuel consumption, more wear on brake linings, increasing driver's mental burden, and causing unexpected collision because of reducing car speed.